RESTful Day 1: Enterprise Level Application Architecture With Web APIs Using Entity Framework, Generic Repository Pattern and Unit of Work

#region Using Namespaces...  

using System;  
using System.Collections.Generic;  
using System.Diagnostics;  
using System.Data.Entity.Validation;  
using DataModel.GenericRepository;  

#endregion  

namespace DataModel.UnitOfWork  
{  
    /// <summary>  
    /// Unit of Work class responsible for DB transactions  
    /// </summary>  
    public class UnitOfWork : IDisposable  
    {  
        #region Private member variables...  

        private WebApiDbEntities _context = null;  
        private GenericRepository<User> _userRepository;  
        private GenericRepository<Product> _productRepository;  
        private GenericRepository<Token> _tokenRepository;  

        #endregion  

        public UnitOfWork()  
        {  
            _context = new WebApiDbEntities();  
        }  

        #region Public Repository Creation properties...  

        /// <summary>  
        /// Get/Set Property for product repository.  
        /// </summary>  
        public GenericRepository<Product> ProductRepository  
        {  
            get  
            {  
                if (this._productRepository == null)  
                    this._productRepository = new GenericRepository<Product>(_context);  
                return _productRepository;  
            }  
        }  

        /// <summary>  
        /// Get/Set Property for user repository.  
        /// </summary>  
        public GenericRepository<User> UserRepository  
        {  
            get  
            {  
                if (this._userRepository == null)  
                    this._userRepository = new GenericRepository<User>(_context);  
                return _userRepository;  
            }  
        }  

        /// <summary>  
        /// Get/Set Property for token repository.  
        /// </summary>  
        public GenericRepository<Token> TokenRepository  
        {  
            get  
            {  
                if (this._tokenRepository == null)  
                    this._tokenRepository = new GenericRepository<Token>(_context);  
                return _tokenRepository;  
            }  
        }  
        #endregion  

        #region Public member methods...  
        /// <summary>  
        /// Save method.  
        /// </summary>  
        public void Save()  
        {  
            try  
            {  
                _context.SaveChanges();  
            }  
            catch (DbEntityValidationException e)  
            {  

                var outputLines = new List<string>();  
                foreach (var eve in e.EntityValidationErrors)  
                {  
                    outputLines.Add(string.Format("{0}: Entity of type \"{1}\" in state \"{2}\" has the following validation errors:", DateTime.Now, eve.Entry.Entity.GetType().Name, eve.Entry.State));  
                    foreach (var ve in eve.ValidationErrors)  
                    {  
                        outputLines.Add(string.Format("- Property: \"{0}\", Error: \"{1}\"", ve.PropertyName, ve.ErrorMessage));  
                    }  
                }  
                System.IO.File.AppendAllLines(@"C:\errors.txt", outputLines);  

                throw e;  
            }  

        }  

        #endregion  

        #region Implementing IDisposable...  

        #region private dispose variable declaration...  
        private bool disposed = false;   
        #endregion  

        /// <summary>  
        /// Protected Virtual Dispose method  
        /// </summary>  
        /// <param name="disposing"></param>  
        protected virtual void Dispose(bool disposing)  
        {  
            if (!this.disposed)  
            {  
                if (disposing)  
                {  
                    Debug.WriteLine("UnitOfWork is being disposed");  
                    _context.Dispose();  
                }  
            }  
            this.disposed = true;  
        }  

        /// <summary>  
        /// Dispose method  
        /// </summary>  
        public void Dispose()  
        {  
            Dispose(true);  
            GC.SuppressFinalize(this);  
        }    
        #endregion  
    }  
}  

Now we have completely set up our data access layer and our project structure looks as shown below.

Setup Business Entities

Remember, we created a business entities project. You may wonder, since we already have database entities to interact with the database, why do we need Business Entities? The answer is as simple as, we are trying to follow a proper structure of communication and one would never want to expose the database entities to the end client, in our case the Web API, it involves a lot of risk. Hackers may manipulate the details and get access to your database. Instead, we'll use database entities in our business logic layer and use Business Entities as transfer objects to communicate between the business logic and the Web API project. So business entities may have different names, but their properties remain the same as database entities. In our case, we'll add the same-named business entity classes appended with the word “Entity” in our BusinessEntity project. So we'll end up having the following three classes.

Product Entity

public class ProductEntity  
{  
    public int ProductId { get; set; }  
    public string ProductName { get; set; }  
}  

Token entity

public class TokenEntity  
{  
    public int TokenId { get; set; }  
    public int UserId { get; set; }  
    public string AuthToken { get; set; }  
    public System.DateTime IssuedOn { get; set; }  
    public System.DateTime ExpiresOn { get; set; }  
}  

User Entity

public class UserEntity  
{  
    public int UserId { get; set; }  
    public string UserName { get; set; }  
    public string Word { get; set; }  
    public string Name { get; set; }  
}  

Setup Business Services Project

Add a new class library to the solution named BusinessServices. This layer will act as our business logic layer. Note that, we can use our API controllers to write the business logic, but I am trying to segregate my business logic in an extra layer so that if in the future I want to use WCF, MVC, ASP.Net Web Pages, or any other application as my presentation layer then I can easily integrate my Business logic layer into it.

We'll make this layer testable, so we need to create an interface and in it declare CRUD operations to be performed over a product table. Before we proceed, add a reference for the business entities project and DataModel project to this newly created project.

Step 1. Create an interface named IProductServices and add the following code to it for CRUD operations methods.

using System.Collections.Generic;
using BusinessEntities;

namespace BusinessServices
{
    /// <summary>
    /// Product Service Contract
    /// </summary>
    public interface IProductServices
    {
        ProductEntity GetProductById(int productId);
        IEnumerable<ProductEntity> GetAllProducts();
        int CreateProduct(ProductEntity productEntity);
        bool UpdateProduct(int productId, ProductEntity productEntity);
        bool DeleteProduct(int productId);
    }
}

Step 2. Create a class to implement this interface. Name that class ProductServices.

The class contains a private variable of UnitOfWork and a constructor to initialize that variable as in the following.

private readonly UnitOfWork _unitOfWork;

/// <summary>
/// Public constructor.
/// </summary>
public ProductServices()
{
    _unitOfWork = new UnitOfWork();
} 

We have decided not to expose our db entities to the Web API project, so we need something to map the db entity's data to my business entity classes. We'll make use of AutoMapper. You can read about AutoMapper in my article.

Step 3. Just right-click the project then select Extension Manager, search for AutoMapper in the online gallery, and add it to the BusinessServices project as in the following.

Step 4. Implement the following methods in the ProductServices class.

Add the following code to the class.

using System.Collections.Generic;
using System.Linq;
using System.Transactions;
using AutoMapper;
using BusinessEntities;
using DataModel;
using DataModel.UnitOfWork;

namespace BusinessServices
{
    /// <summary>
    /// Offers services for product specific CRUD operations
    /// </summary>
    public class ProductServices : IProductServices
    {
        private readonly UnitOfWork _unitOfWork;

        /// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

        /// <summary>
        /// Fetches product details by id
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public BusinessEntities.ProductEntity GetProductById(int productId)
        {
            var product = _unitOfWork.ProductRepository.GetByID(productId);
            if (product != null)
            {
                Mapper.CreateMap<Product, ProductEntity>();
                var productModel = Mapper.Map<Product, ProductEntity>(product);
                return productModel;
            }
            return null;
        }

        /// <summary>
        /// Fetches all the products.
        /// </summary>
        /// <returns></returns>
        public IEnumerable<BusinessEntities.ProductEntity> GetAllProducts()
        {
            var products = _unitOfWork.ProductRepository.GetAll().ToList();
            if (products.Any())
            {
                Mapper.CreateMap<Product, ProductEntity>();
                var productsModel = Mapper.Map<List<Product>, List<ProductEntity>>(products);
                return productsModel;
            }
            return null;
        }

        /// <summary>
        /// Creates a product
        /// </summary>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public int CreateProduct(BusinessEntities.ProductEntity productEntity)
        {
            using (var scope = new TransactionScope())
            {
                var product = new Product
                {
                    ProductName = productEntity.ProductName
                };
                _unitOfWork.ProductRepository.Insert(product);
                _unitOfWork.Save();
                scope.Complete();
                return product.ProductId;
            }
        }

        /// <summary>
        /// Updates a product
        /// </summary>
        /// <param name="productId"></param>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public bool UpdateProduct(int productId, BusinessEntities.ProductEntity productEntity)
        {
            var success = false;
            if (productEntity != null)
            {
                using (var scope = new TransactionScope())
                {
                    var product = _unitOfWork.ProductRepository.GetByID(productId);
                    if (product != null)
                    {
                        product.ProductName = productEntity.ProductName;
                        _unitOfWork.ProductRepository.Update(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
            return success;
        }

        /// <summary>
        /// Deletes a particular product
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public bool DeleteProduct(int productId)
        {
            var success = false;
            if (productId > 0)
            {
                using (var scope = new TransactionScope())
                {
                    var product = _unitOfWork.ProductRepository.GetByID(productId);
                    if (product != null)
                    {

                        _unitOfWork.ProductRepository.Delete(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
            return success;
        }
    }
}

Let me explain the idea of the code. We have the following 5 methods.

To get a product by id (GetproductById): We call the repository to get the product by id. It is a parameter from the calling method to that service method. It returns the product entity from the database. Note that it will not return the exact db entity, instead we'll map it with our business entity using AutoMapper and return it to the calling method.

/// <summary>
/// Fetches product details by id
/// </summary>
/// <param name="productId"></param>
/// <returns></returns>
public BusinessEntities.ProductEntity GetProductById(int productId)
{
    var product = _unitOfWork.ProductRepository.GetByID(productId);
    if (product != null)
    {
        Mapper.CreateMap<Product, ProductEntity>();
        var productModel = Mapper.Map<Product, ProductEntity>(product);
        return productModel;
    }
    return null;
}

Get all products from the database (GetAllProducts): This method returns all the products residing in the database, again we use AutoMapper to map the list and return it.

/// <summary>
/// Fetches all the products.
/// </summary>
/// <returns></returns>
public IEnumerable<BusinessEntities.ProductEntity> GetAllProducts()
{
    var products = _unitOfWork.ProductRepository.GetAll().ToList();
    if (products.Any())
    {
        Mapper.CreateMap<Product, ProductEntity>();
        var productsModel = Mapper.Map<List<Product>, List<ProductEntity>>(products);
        return productsModel;
    }
    return null;
}

Create a new product (CreateProduct): This method takes the product's BusinessEntity as an argument creates a new object of an actual database entity and inserts it using a unit of work.

/// <summary>
/// Creates a product
/// </summary>
/// <param name="productEntity"></param>
/// <returns></returns>
public int CreateProduct(BusinessEntities.ProductEntity productEntity)
{
    using (var scope = new TransactionScope())
    {
        var product = new Product
        {
            ProductName = productEntity.ProductName
        };
        _unitOfWork.ProductRepository.Insert(product);
        _unitOfWork.Save();
        scope.Complete();
        return product.ProductId;
    }
}

I guess you can now write an update and delete methods. So the following is the code for the complete class.

using System.Collections.Generic;
using System.Linq;
using System.Transactions;
using AutoMapper;
using BusinessEntities;
using DataModel;
using DataModel.UnitOfWork;

namespace BusinessServices
{
    /// <summary>
    /// Offers services for product specific CRUD operations
    /// </summary>
    public class ProductServices : IProductServices
    {
        private readonly UnitOfWork _unitOfWork;

        /// <summary>
        /// Public constructor.
        /// </summary>
        public ProductServices()
        {
            _unitOfWork = new UnitOfWork();
        }

        /// <summary>
        /// Fetches product details by id
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public BusinessEntities.ProductEntity GetProductById(int productId)
        {
            var product = _unitOfWork.ProductRepository.GetByID(productId);
            if (product != null)
            {
                Mapper.CreateMap<Product, ProductEntity>();
                var productModel = Mapper.Map<Product, ProductEntity>(product);
                return productModel;
            }
            return null;
        }

        /// <summary>
        /// Fetches all the products.
        /// </summary>
        /// <returns></returns>
        public IEnumerable<BusinessEntities.ProductEntity> GetAllProducts()
        {
            var products = _unitOfWork.ProductRepository.GetAll().ToList();
            if (products.Any())
            {
                Mapper.CreateMap<Product, ProductEntity>();
                var productsModel = Mapper.Map<List<Product>, List<ProductEntity>>(products);
                return productsModel;
            }
            return null;
        }

        /// <summary>
        /// Creates a product
        /// </summary>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public int CreateProduct(BusinessEntities.ProductEntity productEntity)
        {
            using (var scope = new TransactionScope())
            {
                var product = new Product
                {
                    ProductName = productEntity.ProductName
                };
                _unitOfWork.ProductRepository.Insert(product);
                _unitOfWork.Save();
                scope.Complete();
                return product.ProductId;
            }
        }

        /// <summary>
        /// Updates a product
        /// </summary>
        /// <param name="productId"></param>
        /// <param name="productEntity"></param>
        /// <returns></returns>
        public bool UpdateProduct(int productId, BusinessEntities.ProductEntity productEntity)
        {
            var success = false;
            if (productEntity != null)
            {
                using (var scope = new TransactionScope())
                {
                    var product = _unitOfWork.ProductRepository.GetByID(productId);
                    if (product != null)
                    {
                        product.ProductName = productEntity.ProductName;
                        _unitOfWork.ProductRepository.Update(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
            return success;
        }

        /// <summary>
        /// Deletes a particular product
        /// </summary>
        /// <param name="productId"></param>
        /// <returns></returns>
        public bool DeleteProduct(int productId)
        {
            var success = false;
            if (productId > 0)
            {
                using (var scope = new TransactionScope())
                {
                    var product = _unitOfWork.ProductRepository.GetByID(productId);
                    if (product != null)
                    {

                        _unitOfWork.ProductRepository.Delete(product);
                        _unitOfWork.Save();
                        scope.Complete();
                        success = true;
                    }
                }
            }
            return success;
        }
    }
}

The job is now done at the business service level. Let's move on to the API controller to call these methods.

Setup WebAPI project

Step 1. Just add references for BusinessEntity and BusinessService to the WebAPI project, our architecture becomes like the following.

Step 2. Add a new WebAPI controller to the Controller folder. Right-click the Controller folder and add a new controller.

We get a controller as follows.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace WebApi.Controllers
{
    public class ProductController : ApiController
    {
        // GET api/product
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }

        // GET api/product/5
        public string Get(int id)
        {
            return "value";
        }

        // POST api/product
        public void Post([FromBody]string value)
        {
        }

        // PUT api/product/5
        public void Put(int id, [FromBody]string value)
        {
        }

        // DELETE api/product/5
        public void Delete(int id)
        {
        }
    }
}

We get HTTP VERBS as method names. The Web API is smart enough to recognize a request with the name of the VERB itself. In our case, we are doing CRUD operations, so we don't need to change the names of the methods, we just need this. We only need to write the calling logic inside these methods. In my future articles of the series, we will work out how to define new routes and provide method names of our choice with those routes.

Step 3. Add logic to call Business Service methods. Just make an object of the Business Service and call its respective methods, our Controller class becomes like this.

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using BusinessEntities;
using BusinessServices;

namespace WebApi.Controllers
{
    public class ProductController : ApiController
    {
        private readonly IProductServices _productServices;

        #region Public Constructor

        /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController()
        {
            _productServices = new ProductServices();
        }

        #endregion

        // GET api/product
        public HttpResponseMessage Get()
        {
            var products = _productServices.GetAllProducts();
            if (products != null)
            {
                var productEntities = products as List<ProductEntity> ?? products.ToList();
                if (productEntities.Any())
                    return Request.CreateResponse(HttpStatusCode.OK, productEntities);
            }
            return Request.CreateErrorResponse(HttpStatusCode.NotFound, "Products not found");
        }

        // GET api/product/5
        public HttpResponseMessage Get(int id)
        {
            var product = _productServices.GetProductById(id);
            if (product != null)
                return Request.CreateResponse(HttpStatusCode.OK, product);
            return Request.CreateErrorResponse(HttpStatusCode.NotFound, "No product found for this id");
        }

        // POST api/product
        public int Post([FromBody] ProductEntity productEntity)
        {
            return _productServices.CreateProduct(productEntity);
        }

        // PUT api/product/5
        public bool Put(int id, [FromBody]ProductEntity productEntity)
        {
            if (id > 0)
            {
                return _productServices.UpdateProduct(id, productEntity);
            }
            return false;
        }

        // DELETE api/product/5
        public bool Delete(int id)
        {
            if (id > 0)
                return _productServices.DeleteProduct(id);
            return false;
        }
    }
}

Just run the application and we will get it.

But now how do we test our API? We don't have a client. Guys, we'll not be writing a client now to test it. We'll add a package that will do all the work.

Just go to Manage Nuget Packages by right-clicking WebAPI project and type WebAPITestClient into the search box in online packages as in the following.

You'll get “A simple Test Client for ASP.NET Web API”, just add it. You'll get a help controller in Areas -> HelpPage as shown below.

Running the Application

Before running the application, I put some test data in our product table.

Just hit F5, and you get the same page as you got earlier, just append “/help” to its URL and you'll get the test client as in the following:

You can test each service by clicking on it.

Service for GetAllProduct

To create a new product.

In the database, we get a new product as in the following.

Update product.

We get the following in the database:

Delete product.

In the database.

Job done.

Design Flaws

1. The architecture is tightly coupled. Inversion of Control (IOC) needs to be there.
2. We cannot define our own routes.
3. No exception handling and logging.
4. No unit tests.

Conclusion

We now know how to create a WebAPI and perform CRUD operations using an n-layered architecture.

But still, there are some flaws in this design. In my next two articles, I'll explain how to make the system loosely coupled using the Dependency Injection Principle. We'll also cover all the design flaws to make our design better and stronger. Until then Happy Coding. You can also download the source code from GitHub.

Read more

• C# and ASP.NET Questions (All in one)
• MVC Interview Questions
• C# and ASP.NET Interview Questions and Answers
• Web Services and Windows Services Interview Questions

For more technical articles you can reach out to CodeTeddy

My other series of articles,

• Learning MVC
• Learning OOP concepts with C#